1. Field of the Invention
The present invention relates to printing rollers and, more particularly, to printing rollers on which a sleeve can be precisely aligned.
2. Description of the Prior Art
In modern sleeve technology, that is, in techniques for channel-free printing--specifically with a rubber blanket and printing form--the sleeve-shaped printing form or transfer form is conventionally applied to a printing roller by expanding the printing form or transfer form using compressed air and slipping the printing form onto the printing roller. When the compressed air is removed, the printing form or transfer form contacts the printing roller in a positive engagement based on the principle of a shrinkage fit. The printing form or transfer form can be removed again from the printing roller by once again supplying compressed air. As a rule, such a printing roller is normally manufactured from a metallic work material and preferably has a chrome coating to protect it from corrosion due to commonly used media.
A printing roller of this kind is known from the German Patent Application P 43 42 159.8. This patent application describes a sleeve-shaped printing form. The sleeve, whose inner diameter is smaller than the diameter of the supporting part of the cylinder, is mechanically widened to obtain a diameter at least equal to the diameter of the supporting part of the cylinder prior to pre-centering using a conical chamfer positioned at an entry end of the printing roller body so that the sleeve can be completely slid onto the roller body. A supply of compressed air passing through outlet bores on the cylinder provide an air cushion acting to increase the diameter of the sleeve and aid in positioning the sleeve on the roller body.
Further, it is known in today's printing industry to use plastic sheets as a base for adjusting or aligning conventional rubber blankets and printing forms in plate form, as well as for lengthening and reducing the printed image. However, such plastic sheets as known in the art are not applicable for use with sleeve technology.